The effects of dopant and sintering atmosphere on abnormal grain growth of $SrTiO_3$ have been investigated. The microstructures of $Nb_2O_5$ and/or $Al_2O_3$-doped $SrTiO_3$ were observed after sintering in an oxidizing(air) or a reducing ($5H_2-95N_2$) atmosphere. Specimens were sintered at 1480℃ for various times from 5 min to 4 h. In case of undoped $SrTiO_3$ specimens, normal grain growth occurred independently of sintering atmosphere. For $Nb_2O_5$-doped $SrTiO_3$ specimens, normal grain growth occurred in air and abnormal grain growth in $5H_2-95N_2$. For $Al_2O_3$-doped $SrTiO_3$ specimens, abnormal grain growth occurred in air but not in $5H_2-95N_2$. When the same amount of $Nb_2O_5$ and $Al_2O_3$ was codoped, normal grain growth occurred independently of the sintering atmosphere similar to the case of undoped $SrTiO_3$ specimen. These experimental observations were discussed in view of the concentration of lattice defects, the interfacial segregation of dopants and the amount of liquid.
